There are many situations in which signals must be quantized. Quantizing is here defined by example: the numbers 0, 1, 2, 3, 4, 5, can represent the quantum levels (or threshold levels) used for quantizing a signal. The signal itself, however, may have any value between 0 and 5, including a fractional value such as 2.5. Quantizing (sometimes called digitizing) ascribes a value to, or "rounds off," a signal whose value falls between, and not exactly on, the quantum levels. The value ascribed to the signal can be the value of the largest quantum level which the signal value equals or exceeds. Thus, signals of values 1.25, 2.75, and 4 would be ascribed values of 1, 2, and 4 as output signals, respectively.
In some situations, it is desirable to provide a signal quantizer having adjustable threshold levels and, further, having a means for adjusting the quantized output signals.
For example, as shown in FIG. 1, which is a schematic diagram of the present invention shown in conjunction with the invention of D. Copley (more fully identified below in the Detailed Description of the Invention), a machine-tooled workpiece 3 can be scanned by a movable eddy current probe or other inspection transducer 6 which produces an electrical signal indicative of surface features contained on the workpiece 3. This signal is carried by a conduit 9 to a signal processor 12 which converts the signal to a direct current signal 13 which is transmitted along conduit 15, through switches 16A and 16B, and to a power amplifier 19 which amplifies the direct current signal 13 and transmits an amplified signal 20 along conduit 22 to an electrode pen 25. A point 27 of electrode pen 25 is in contact with a record paper 30 which is connected to ground by a conduit 33. The current signal carried by conduit 22 and traveling through record paper 30 generates heat at the point of contact 27 between electrode pen 25 and record paper 30 and this heat produces a small burn mark in record paper 30. Variations in the signal present on conduit 22 induced by variations in the signal produced by the eddy current transducer 6 cause variations in the degree of burning and thus produce variations in the color of the mark burned into record paper 30.
In practice, the eddy current probe 6 is moved with respect to the machine-tooled workpiece 3 by mechanical devices (not shown) and, simultaneously, the electrode pen 25 is mechanically moved with respect to record paper 30 in a corresponding manner. Thus, the scanning path of the probe 6 along workpiece 3 is mapped identically and to scale onto record paper 30 by the burn marks produced by electrode pen 25. Accordingly, variations in the surface features of workpiece 3 are mapped and indicated by burn marks present on record paper 30.
A problem arises in the use of this system because the signal, produced by the eddy current probe 6, is generally a continuously varying analog signal. Thus, the burn marks produced are similarly varying along a color spectrum ranging from white or light gray to dark gray or black. A particular problem found will be illustrated by example.
It is assumed that the color spectrum can be represented by a number sequence from 0 to 10 in which 0 represents white or light gray and 10 represents black or dark gray. Two colors, such as colors 5 and 6, can be adjacent on record paper 30, but the difference in grayness between them can be difficult to distinguish because the color darkens continuously from the location of color 5 to that of color 6. There is no clear line of demarcation. Thus, it is difficult to interpret the burn marks produced by eddy current probe 6 in this case.
Another problem arises in analyzing burn marks recorded upon different types of record papers or upon record papers of the same type but at different times. In the former situation, the differences in record papers can cause identical eddy current probe signals to produce different burn marks. In the latter situation, differences in the environment, such as humidity or temperature differences, occurring at the different times, can similarly cause nonuniform burn marks to result from identical probe signals. In both situations, it is difficult to compare the different records of eddy current signals.